Fabrication of a high-power semiconductor package assembly (e.g., >10 watts power dissipation) typically begins with attaching a semiconductor die to a heat dissipating member (or “heatsink”), which also may function as the ground plane of the device. In many cases, the heatsink forms a portion of a leadframe, and fabrication further includes connecting wirebonds between the leadframe leads and the die, and encapsulating the assembly with a plastic encapsulant.
The above-described type of package assembly is adequate for many devices. However, it has several limitations and drawbacks that make it less suitable for some types of high power, radio frequency (RF) semiconductor devices. Such a device may include at least one input lead, at least one output lead, a high-power transistor die, and wirebond arrays coupling the input and output leads to the transistor die. The wirebond arrays have significant inductances at high frequencies. Accordingly, to ensure adequate impedance matching at the device input and output, additional passive components (e.g., capacitors, inductors, and so on) may be included within the device. For example, additional discrete capacitors and/or inductors may be electrically connected between a transistor die and the input and/or output leads prior to encapsulation. Whether the passive components are directly coupled to the heatsink or are located above the heatsink, the proximity of the heatsink to the passive components may detrimentally affect the quality factor (Q) of the components.
In addition, relatively expensive leadframes typically are used in high power semiconductor devices because the power dissipation requirements may necessitate the use of relatively thick heatsinks. In single gage leadframes, the leads and the heatsink are the same thickness (e.g., about 0.5 millimeters (mm) or more). Alternatively, a dual gage leadframe includes leads and a heatsink with different thicknesses (e.g., leads with thicknesses of about 0.2 mm and a heatsink with a thickness of 0.75 mm or more). Both the thick, single gage leadframe and the dual gage leadframe may be several times more expensive than a typical low power device leadframe.